The present invention relates to the field of microelectronic devices, and more particularly to methods for reducing the chloride content of epoxy compound starting materials which are subsequently used to formulate encapsulants and underfills for microelectronic devices.
Microelectronic devices are useful in a variety of consumer and industrial applications. Microelectronic devices are prepared utilizing a variety of chemical formulations, e.g., encapsulants and/or underfills. A typical component of encapsulants and underfills is a compound having at least one epoxy reactive group. A common impurity of such epoxy-containing compounds is chloride. Unfortunately, chloride is known to corrode the wire bonds within microelectronic devices. Thus, a major problem associated with microelectronic devices is the tendency of certain residual impurities (e.g., chloride) within the microelectronic devices to decrease the reliability of the device by promoting the corrosion of the wire bonds within the device, thereby increasing the risk of the device""s failure.
There are only limited examples of the use of distillation to purify epoxy resins. Previously described distillation methods to purify epoxy resins suffer from several limitations. For example, known methods do not substantially reduce chloride content. In addition, known methods have only been described with respect to specifically defined diepoxides. Thus, there is no suggestion in the prior art that such methods are generally applicable to epoxides as a class.
Further, known methods require elevated temperatures. These elevated temperatures increase the risk of homopolymerization of the epoxy resin, which will lead to increased viscosity thereof, and reduced processibility of the encapsulant and/or underfill made therefrom. Moreover, these elevated temperatures increase the risk of side reactions of the epoxy resin, which will lead to decreased purity of the specifically defined diepoxide. Alternatively, prior art methods may require heat transfer and/or residence time which are insufficient to promote the requisite purification of the epoxy resin.
Accordingly, there remains a need in the art for new and better methods of reducing chloride content of epoxy compounds, particularly those used as starting materials in the formulation of electronic materials for the assembly of microelectronic devices. In addition, there is a need for epoxy compounds having reduced chloride content. Further, there is a need to ensure that these epoxy compounds do not suffer from increased viscosity.
In accordance with the present invention, there are provided methods for the reduction of the chloride content of epoxy compound starting materials. Invention methods comprise fractionating an epoxy compound starting material into portions (e.g., fractions or cuts) having different chloride content relative to the epoxy compound starting material. Certain of these collected portions (i.e., the portions fractionated and collected after collection of the forecut and before discontinuation of the fractionation) contain substantially reduced chloride levels relative to the epoxy compound starting material.
In an additional aspect of the present invention, there are provided reduced chloride content epoxy compounds produced by invention methods.
In a further aspect of the present invention, there are provided methods for producing a reduced viscosity formulation made from a treated epoxy compound, wherein the reduced viscosity formulation has a reduced viscosity relative to an analogous formulation made from an epoxy compound starting material. Invention methods comprise fractionating an epoxy compound starting material (e.g., an epoxy diluent, an epoxy resin, and the like) into portions (e.g., fractions or cuts) having different viscosities relative to the epoxy compound starting material. Surprisingly, formulations for encapsulants and/or underfills made from certain of these collected portions (i.e., the portions fractionated and collected after collection of the forecut and before discontinuation of the fractionation) exhibit substantially reduced viscosity levels relative to analogous formulations for encapsulants and/or underfills made from the epoxy compound starting material. Typically, the reduced viscosity formulations made from the collected portions also contain substantially reduced chloride levels relative to the corresponding formulations made from the epoxy compound starting material.
The present invention provides many advantages over the art. For example, invention methods and compounds are useful in preparing more reliable microelectronic devices. In addition, invention methods which reduce the viscosity of a formulation are useful in increasing the processibility of the formulation utilized in the preparation of microelectronic devices, thereby decreasing the cost of the prepared device and reducing the incidence of device failure. Other advantages of the present invention can be readily recognized by those of ordinary skill in the art.